Automated liquid handling systems have become a standard part of many biological laboratories. In a typical configuration a robot or motion system is coupled with a syringe or peristaltic pump (such as the Biomek configuration by Beckman Coulter, Inc.). Such systems are fairly effective in transferring liquid samples in the 1 .mu.l or larger range from one container to the other. However, they do not generally provide reliable transfer of sample volumes smaller than 1 .mu.l.
Devices are known for through pumping of small fluid quantities. For example, U.S. Pat. No. 5,094,594, U.S. Pat. No. 5,730,187 and U.S. Pat. No. 6,033,628 disclose devices which can pump fluid volumes in the nanoliter or picoliter range. However, these devices are arranged so that the fluid sample is pumped through them. Such devices are not convenient for simply transferring fluid from one container to another where it is desired to aspirate and expel the fluid from the same opening in the manner of a pipette. This is so since with very small fluid samples some of the fluid will wet and remain in the pumping mechanism itself. The pumping mechanism then, becomes a source of sample cross-contamination unless cleaned.
It would be desirable then if a means could be provided which allowed for transfer of very small samples of relatively precisely controlled volume. It would further be desirable if such means allowed the surfaces contacted by the fluid to be separable and replaceable from the remainder of the device.